The reed in a loom, for example an air jet weaving loom, comprises a multitude of profiled reed dents that are assembled in and held by a reed frame including an upper and a lower reed frame rail. The upper ends of the reed dents are held in the upper rail while the lower reed dent ends are held in the lower rail. The plurality of the recesses, one of which is formed in each reed dent, form the weft thread insertion channel. The recesses have, for example a U-shaped configuration. The weft thread insertion channel is open toward the beat-up edge, whereby the back wall of the individual recess in each dent beats the weft thread against the beat-up edge to bind the weft thread into the fabric. Each recess in each dent also has an upper edge and a lower edge merging into the back wall. These edges and the back wall are exposed to frictional abrasion when the weft thread moves through the insertion channel. The back wall or back edge is especially exposed to wear and tear when the weft thread is beat up against the beat up edge. Thus, the surface areas forming the just mentioned edges are exposed to increased wear and tear, whereby conventional dents have a useful life time of about 1000 hours of operation. These considerations apply equally to the reed dents in a gripper loom in which the reed guides the grippers for the weft insertion.
The operational time of about 1000 hours requires making the reed dents of high quality alloyed steels. Yet reed dents made of such steels must be replaced after about 1000 hours of operation. Such replacement is undesirable, not only because it is increasing the costs of operating a loom, the replacement requires dead times in which the loom cannot produce.
Reed dents have been made heretofore of cold rolled strip steel made of steel selected from the group of X 12 CrNi 177; X 5 CrNiMo 1810; or X 7 CrNiAl 177. The details of the alloying components of these steels are described in information sheets of German Industrial Standards DIN 17224, February 1992. The dents are stamped out of the strip steel. These steels have a material strength of about 1200N/mm.sup.2 providing a useful lifetime for the dents of about 1000 hours.
TABLE __________________________________________________________________________ Chemical Composition of the above Steels (Melt analysis) Steel Grades Chemical Composition (% by weight) (1) Material C Si Mn Short Name Number max. max. max. Al Cr Mo Ni __________________________________________________________________________ X 12 CrNi 177 1.4310 0.12 1.5 2.0 -- 16.0 to 18.0 .ltoreq.0.8 6.0 to 9.0 X 5 CrNiMo 18 10 1.4401 0.07 1.0 2.0 -- 16.5 to 18.5 2.0 to 2.5 10.5 to 13.5 X 7 CrNiAl 177 1.4568 0.09 1.0 1.0 0.75 to 1.50 16.0 to 18.0 -- 6.5 to 7.75 __________________________________________________________________________ (1) For all grades .ltoreq.0.045% P and .ltoreq.0.030% S.
German Patent Publication DE-OS 2,220,859 (Schreus et al.) published on Dec. 13, 1973, discloses a reed dent having a locally limited hardened zone. This zone is particularly limited to the edges or front surfaces of the dent. The hardened zones are made either by a localized hardening or by coating these areas with a hard material if the steel of the dent itself is made of ordinary, non-refined steels. However, details of achieving the localized hardened areas are not disclosed. It has been found that the intended increase of the useful operating time of dents has not been achieved if the hardening in localized areas takes place conventionally.
It is also known to treat reed dents galvanically, for example to achieve a hard chrome galvanically deposited coating. Conventional dents having a thickness within the range of about 0.15 mm to about 0.8 m mare provided with a hard chrome coating having a coating thickness of about 10 .mu.m. This coating has a hardness according to Vickers of about 700 HV. These hard chrome coatings increase the useful life of the dents to twice the hours normally achieved. This holds true even when the weft threads have a substantial abrasive quality. Weft threads such as jute, fiberglass yarns, fiberglass rovings and the like have such abrasive characteristics.
It has been found that reed dents provided with a hard chrome coating require a surface treatment following the coating in order to provide a smooth surface. The chrome coating itself results in a rough surface at the upper and lower edges and the back wall edge forming the individual recess in each dent. Performing the surface coating by galvanic deposition for example in these areas involves additional efforts and expense.
Swiss Patent Publication CH-PS 671,034 (Ischii et al.) published on Jul. 31, 1989, discloses machine components exposed to elongated fibrous members such as yarns or threads used in a loom, knitting machines, and the like. The exposed components are, for example heddles, relay nozzles, reed dents, and the like made of stainless steel and coated with a chrome oxide Cr.sub.2 O.sub.3 layer. The coating is made by dipping the components into a solution containing chrome, for example an aqueous solution of CrO.sub.3 to coat the components, whereupon a heat treatment is performed to achieve a reaction in a temperature range of about 500.degree. to 600.degree. C., whereby a surface coating is formed in which the main coating proportion is Cr.sub.2 O.sub.3.
Swiss Patent Publication 671,034 further discloses that a porous ceramic layer may be formed by applying a coating of a chrome containing composition including abrasion resistant particles such as aluminum oxide Al.sub.2 O.sub.3 or silicon oxide SiO.sub.2 particles. These treatments achieve a Vickers hardness of 500 HV or more. As is generally known, chrome coatings have a Vickers hardness of about 700 HV but require an after-treatment as mentioned above. Such an after-treatment should be avoided.
European Patent Publication 0,550,752 (Miya et al.) published on Jul. 14, 1993 discloses a reed for a high speed loom. The dents of the reed are provided with a diamond-like carbon (DLC) coating or film on dents made of stainless steel. First, the dents are provided with an intermediate coating for improving the bonding of the diamond-like carbon film on the surface of the dents. The bonding improving coating is a titanium carbide alloy. Once the intermediate coating has been applied, the diamond-like carbon film is applied by chemical vapor deposition in a reaction chamber at a certain pressure and certain temperature under which the dents are contacted by a hydrocarbon gas providing the source for the diamond-like carbon. It has, however, been found that the diamond-like carbon film does not provide the expected improvement in the wear resistance, the fatigue strength, and the alternating bending strength of the dents. Thus, even this approach leaves room for improvement.
It is further known from a German Industrial Standard (DIN) Handbook No. 155 "Quality Standards for Steel and Iron" No. 2, 1985, pages 119 and 120, published by Beuthverlag GmbH Berlin and Cologne, Second Edition, that the material strength can be increased for the above mentioned steel types by a heat treatment involving a single aging or annealing operation or by a double aging or annealing operation. For example, it is possible to obtain a material strength of 1400N/mm.sup.2 if the dents are made of X 7 CrNiAl 177 steel having a thickness of 0.75 mm if the heat treatment takes place at a temperature within the range of 480.degree. C. to 550.degree. C. for a duration of 1 to 2 hours at the most. This treatment results in a 15 to 25% increase in the material strength as compared to that of a steel of the same chemical composition, but without heat treatment.
In connection with the manufacture of tools, it is also known to provide the tool surfaces with a thin layer of high hardness, for example a titanium nitride layer. These layers are deposited out of the gas phase by ion implantation or by a sputtering deposition. The hard surface layers are relatively thin, yet expensive to form. Due to the large number of required reed dents it would appear that these methods are not suitable for the manufacture of reed dents or other loom components exposed to frictional abrasion such as weft thread brake lamellae.